Variable resistance unit



Jan. 24, 1939. L E. LAWRENCE Er AL 2,144,925

VARIABLE RES I STANGE UNIT Filed July 2, 1937 NVENTQRS fil Patented Jan. 24, 1939 UNIT-ED STATES PATENT OFFICE VARIABLE RESISTANCE UNIT Leland E.'Lawrence and Robert 0. Lewis; In-

dianapolis, Ind., assignors to P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware lApplicmtion July 2, 1936, Serial No. 88,552

' s clam (C1. en -ssi YThis invention relates to variable resistance dehumidity. The base is preferably made of a vices and more particularly to variable resistances porous fibrous material such as paper and is imcomprising a layer of resistance material on a pregnated with a material which has a high resupporting base. sistance to humidity, preferably a gelatinizing An object of the invention is to improve a varioil such as tung oil. able resistance device. Referring to the drawing a variable resistance Another object is to improve a resistance eledevice is illustrated in Figures l and 2 embodyment andthe base thereof. ing a resistance element made according to the Other objects of the invention will be apparent present invention. The variable resistance device vfrom the following description and accompany- 20 comprises a base formed of two superimposed ing drawing taken in connection with the appended claims.

The invention comprises the features of construction, combination of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the drawing. l

In the drawing:

Figure 1 is a face view of a variable resistance device with the cover thereof removed;

Figure 2 is a section on the line 2-2 of Figure 1, but with the cover in place; and

Figure 3 is a perspective view of the resistance element for said variable resistance device.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the construction of parts without departing from the spirit ofthe invention. In the following description and inthe claims, parts will be identified by specic names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Variable resistance devices have been made heretofore having a resistance element comprising a disc or ring of insulating Vmaterial upon which is a coating or layer of resistance material such as carbon paint. The insulating materials used for the ring base have-been of two types, hard An example of a hard base material is akelite fibre. The most common soft material has been porous paper of the nature of blotting paper. The hard base material provides a unit which is fairly constant under different conditions of humidity but is somewhat noisy in opera-4 tion. The soft base, on the other hand, produces a volume control which is' more quiet in operation, but its humidity coelcient is higher.

v According to one aspect of the present invention a base for a resistance element is provided which has the inherent softness which gives quiet operation and also issubstantially unaffected by pregnated with a synthetic resin. Discs 2l and 22 each have suitable cutout portions to accommodate other parts of the resistor structure. A metal cover or cap I9 is secured to the discs 2| and 22 by ears l9a and encloses the operating parts.

The resistance element of the device, namely ring 23,' is mounted against' the face of disc 22. According to the preferred form of the invention ring 23 comprises a laminated paper base, such as that illustrated in Figure 3, having a layer 24 of resistance paint, such as graphite or other carbon or metal particles, conductive oxide parposited on its surface.

The element may also preferably be provided with a pair of conductive terminals 25 and 26 at the two ends of the resistance layer and in electrical contact with the same. Terminal 25 and 26 may be of conductive paint, such as silver particles in a sheliac binder.

The base itself preferably comprises three 1aminae which are all adhered together into a single unitary sheet, the backing lamina being of litho paper, the center of newsprint paper and the face being of manila paper. It is Vfound that this particular combination of papers results in a unit which is substantially flat after impregnation and coating with resistance paint.

In making the resistance elements ringsv of the shape shown in Figure 3 are punched from the laminated paper described above and soaked in a Solution consisting of about 10% or 15% raw tung oil in a suitable volatile solvent, such as naphtha, for about one hour. a

The tung oil used is preferably oilwhich has not been treated by heat-polymerization or the addition of chemicals to render it nongelatinizing. In carrying out the present invention the gelatinizing property of the raw tung oil is utilized and accordingly it is desired that the oil be in such a condition that it will jell upon heating to ticles or the like in a binder such as sheliac deu upon which the resistance surface is deposited discs 2l and 22 of insulation, such as fibre imthe normal gelatinizing temperature, usually between 200 C. and 300 C. While tung oil is preferred other gelatinizing oils of similar character may also be used.

When the rings have been removed from the impregnating solution they are dried in the air for two hours or more and then baked in a suitable oven at the gelatinizing temperature, such as 210 C. to 250 C. for a period of fteen to thirty minutes. The oil is thereby gelatinized within the pores of the paper thus greatly improving its humidity coeicient but remains' soft and jellylike or rubbery in nature so that the paper remains pliable and resilient. This gives a cushioning effect to the finished unit resulting in very quiet operation.

If desired the,above operations could be carried out on the paper in sheet form and the rings could then be punched from the sheets after the above baking is finished.

'I'he resistance layer 24 is next applied by spraying or otherwise and may be so tapered in thickness, width or composition as to give the desired resistance vs. degree of rotation curve in the variable resistance device. The conductive paint terminals are then appliedby spraying or f painting and the unit is dried and again baked 'at a temperature sufficient to cure and harden the resistance surface, such as at 220 C. It has been found that the laminated paper bases will warp slightly after impregnation but that the application of the resistance surface layer apparently has an opposing effect which causes the rings to flatten out again. The rings may then be assembled into resistance devices of the type illustrated.

It is also contemplated that the resistance surface could be formed of resistance material suspended in tung oil which is gelatinized on the surface of the ring base.

Terminal bolts 21 and 28 passthrough ring 23 and base disc 22 and are in electrical contact with terminal coatings 25 and 26, respectively. Ter-P minal lugs 29 and 30 are secured by bolts 21 and 28, respectively, underneath disc 22 and project f out beyond the base to provide for external circuit lconnections to the two ends of the resistance surface. Bolts 21 and 28 not only serve as terminals but likewise clamp the ring 23 to base disc 22.

Discs 2| and 22 are clamped together at their centers by a metal bushing 32 which passes through these members and a metal disc 33 v clamped against the back of disc 2| by bushing 32.

A metal contact ring 34 having an integral terminal lug 35 is mounted against the face of disc 22 within the resistance unit ring 23 and concentric therewith. Ring 31 is heldin place by a rivet or eyelet 36 which clamps disc 2| and lug 35 together.

The variable contactor structure comprises a shaft 31 rotatable in bushing 32, a contact arm 38 secured to the end of shaft 31 on the face side of said resistance device, a sliding contactor 40 mounted on the end of said arm and adapted to slide on resistance surface 24 on ring 23, and

- sliding contact ngers 39 integral with said arm and adapted to slide on contact ring 34. Shaft 31 is held against axial motion by clip washer 3| fitted in an annular groove in shaft 31 adjacent the rear end of bushing 32. Contact arm 38 is secured vto the end of shaft 31 and insulated therefrom by a small piece of sheet insulation 4| the end of said shaft being upset to hold said piece 4| in place. Contact arm 38 and piece 4| are clamped together by a rivet pin 42. Pin 42 has a projecting portion 43 for operating a switch element which may be secured to the cover, if desired, so that the switch actuating lever is engaged by projection 43. Arm 38 and contact ngers 39are of spring construction and are held in tension by clip washer 3| so that the sliding contact portions` are held in contact with their respective ring surfaces.

In operation, the terminal lugs 23, andA 35 are connected into an external circuit in any desired manner. By turning shaft 31 with a knob or other control means sliding contactor 48 will slide on the resistance surface 24 in a circular path. Thus the length of the resistance path,

'and consequently the magnitude of the resistance in series with terminal lugs 29 and 35 or 30 and may be varied. Conductive coating 26 extends out a sufiicient distance from terminal bolt 21 so that contactor may ride up onto it as it approaches the terminal, thereby reducing the resistance to a negligible value. This enables the turning of arm 38 for a few degrees at the end of the stroke to allow for a switch to be operated by projection 43 on pin 4.2, if desired, without varying -the resistance. The contact arm may be turned until it comes into direct contact with the screw 28 connected tovlug 30, thereby reducing the resistance to substantially zero.

The resistance units made according to this invention are extremely quiet in operation and substantially free from change due to humidity variations. The sliding contact is cushioned by the resilient impregnated paper unit making its movement very smooth and quiet, the contactor making for itself a polished smooth path in the matte surface of the resistance layer.'

While the present invention, as to its objects and advantages, has been described herein as carried out in speciflc embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. A resistance element for variable resistance devices of the type utilizing a moving contactor engaging the resistance surface, said element l comprising a base of porous flexible vinsulating material impregnated with a gelatinized insulating oil, said oil being resilient and substantially unaffected by normal operating conditions encountered by the variable resistance device in radio circuits, whereby said base is capable of permanently maintaining its resiliency under normal operating conditions.

2. A variablev resistancel device comprising a base, a resistance layer on said base and a moving contactor adapted to move over said resistance layer in contact therewith, said base comprising a porous flexible material impregnated with gelatinized tung oil.

3. A variable resistance device comprising a iis fis

per center and a manila. paper face upon which said resistance surface is held.

6. A resistance element comprising a paper base and a resistance surface thereon, said base comprising a litho paper back, a newsprint paper center and a manila paper face upon which said resistance surface is held, said base being impregnated with a gelatinized oil.

7. A resistance element for variable resistance devices ci' the type utilizing a moving contacter engaging a resistance surface, said element comprising a base of porous ilexible insulating material impregnated with water proof insulating jelly capable of permanently maintaining its jelly-like consistency under the normal operating conditions encountered by variable resistance devices in radio circuits.

8. A resistance element for a variable resistance device of the type utilizing a moving contactor engaging a resistance surface, said element comprising a porous ilexible sheet base of ilbrous insulating material impregnated with a water-proof insulating jelly capable of permanently maintaining its jelly-like consistency under the normal operating 'conditions encountered by variable resistance devices in radio circuits.

LELAND E. LAWRENCE. 

